(1) Field of the Invention
This invention relates to the drilling of wells into subterranean strata containing high temperature fluids such as aqueous geothermal fluids or brines. More particularly, this invention relates to an improved aqueous gas-containing drilling fluid composition and method of use thereof which composition provides improved protection against corrosion of the well conduit and other metal parts of the well apparatus which are exposed to the drilling fluid.
(2) Description of the Prior Art
Drilling wells into subterranean strata containing a high temperature fluid presents many problems concerning the choice of a drilling fluid. Conventional aqueous base drilling fluid containing water, clay and various additives is generally used in drilling the first two to four thousand feet of hole through the usually somewhat incompetent strata above the strata containing the high temperature fluid. Casing is cemented in place over this portion of the hole and drilling is continued using any one of a number of drilling fluids. Problems arise at lower depths when the drill bit penetrates those strata containing a high temperature fluid, which formations often lie several thousand feet below the surface. Such formations are sometimes highly porous and permeable. If conventional drilling fluid is used, the weight of the high gravity column of drilling fluid in the well is so great that a considerable amount of the fluid invades the formation. This necessitates use of a large additional volume of fluid and results in partial plugging of the formation by the clay and other solids in the fluid. When the well is subsequently completed, this plugging decreases the amount of fluid which can be produced via or injected into the well. If a relatively light-weight drilling fluid, such as air or another gas, is used, a high rate of circulation of the drilling fluid through the system is required to circulate cuttings out of the hole. This high rate of circulation of the drilling fluid together with the fluids produced from the formation, result in corrosion and erosion problems. The high velocity gaseous fluids erode the unconsolidated portions of the formation to such an extent that hole stability cannot be achieved. In many cases, even the drill pipe is eroded.
One solution to these problems has been to drill formations containing a high temperature fluid with aqueous gas-containing drilling fluid. Use of this light-weight, gas-containing drilling fluid comprising a mixture of water, a gas such as air, a fluid loss control additive, an additive to improve wall-building and cuttings-carrying properties, and optionally a foaming agent, results in increased penetration rates, reduced bit wear and reduced formation damage due to erosion by the drilling fluid as compared with air. However, the metal well equipment exposed to such circulating gas-containing drilling fluid in a high temperature environment is subject to severe corrosion caused by various components in the drilling fluid as well as various fluids entering the well from the surrounding strata.
U.S. Pat. No. 3,653,452 to Fischer et al. issued Apr. 4, 1972 describes a method of gas drilling a high temperature formation using an ammonium or an amine salt of a tertiary amine having a molecular weight above 260 as an additive to the gas stream as an erosion and corrosion inhibitor. At elevated temperatures of 250.degree. F. and above, the additive releases ammonia or a vaporous amine which forms a resinous residue on the well equipment.
Pending U.S. patent application Ser. No. 639,652 by Fischer et al. filed Dec. 11, 1975, now U.S. Pat. No. 4,013,568, describes an aerated drilling fluid for drilling geothermal strata which drilling fluid contains the same ammonium or amine salts. However, in drilling many strata containing a high temperature fluid with this particular aerated drilling fluid, considerable corrosion of the well equipment still occurs.
U.S. Pat. No. 3,307,625 to Johnson et al. issued Mar. 7, 1967 describes an aqueous base drilling fluid containing an inhibitor to control corrosion due to hydrogen sulfide encountered during drilling. The drilling fluid contains an amount of caustic which is sufficient to maintain the pH of the drilling fluid above 7, plus enough alkali metal sulfide to raise the pH above 9.
U.S. Pat. No. 2,496,594 to Moyer et al. issued Feb. 7, 1950 discloses a method of inhibiting corrosion of oil field equipment exposed to crude oil -- brine mixtures by adding thereto a mixture of formaldehyde and ammonia or an amine.
U.S. Pat. No. 2,889,276 to Barrett et al. issued June 2, 1954 describes volatile aliphatic amines as vapor phase corrosion inhibitors for oil well casing and tubing exposed to liquids and vapors containing hydrogen sulfide and water.
While the corrosion inhibitor-containing fluids described in the foregoing patent application and patents have certain utility, need remains for an inhibitor to provide improved corrosion control to the entire system of oil field equipment exposed to gas-containing drilling fluid during the drilling of strata containing high temperature aqueous fluids.
Accordingly, a principal object of this invention is to provide a gas-containing drilling fluid composition and method for drilling strata containing high temperature fluids.
A further object of the invention is to provide such a composition and method wherein the metal well equipment exposed to the composition during drilling is protected against corrosion.
A still further object of the invention is to provide such a composition and method wherein the protection against corrosion is provided to the metal well equipment exposed to such a composition in either the liquid or vapor phase.
Another object of the invention is to provide such a composition which contains both a vapor phase corrosion inhibitor and a liquid phase corrosion inhibitor.
Still another object of the invention is to provide a corrosion inhibitor-containing drilling fluid composition and method for drilling strata containing a geothermal fluid.
An additional object of the invention is to provide a corrosion inhibitor-containing drilling fluid composition and method for drilling strata containing both hydrocarbons and a high temperature brine.
Other objects, advantages and features of the invention will become apparent from the following description and appended claims.